1. Field of the Invention
The present invention relates to a method for ejecting a liquid, a liquid ejection head and a liquid ejection apparatus.
2. Description of the Related Art
A so-called piezo type liquid ejection head is commonly used, which includes a nozzle that ejects liquid, a pressure chamber connected to the nozzle, and a piezoelectric element that causes the liquid to be ejected from the nozzle by changing the volume of the pressure chamber.
A so-called bubble jet type of liquid ejection head is also known, which ejects liquid from a nozzle by creating a bubble by heating the liquid.
Japanese Patent Application Publication No. 2003-094662 discloses a composition in which a gas channel for introducing gas in a direction perpendicular to the direction of ejection is arranged inside the nozzle, in such a manner that the liquid is previously split off inside the nozzle flow channel before the start of the ejection operation.
In a piezo type of liquid ejection head, in general, a drive signal of a pull-push-pull waveform is applied to the piezoelectric element so as to pull, push and pull the liquid in the nozzle to eject one droplet of the liquid. The beneficial effects of tearing off a liquid column protruding from the nozzle by means of final “pull” part of the waveform are important in creating a minute droplet, avoiding satellite droplets, and achieving high-speed output. As shown in FIG. 17, however, while the liquid column 34 keeps growing, the part connected to a meniscus (air-liquid interface) 31 in a nozzle 51 is pulled toward the nozzle. As a result of this, the ejection speed falls. Furthermore, a speed differential is produced between the leading portion of the liquid column and the tail portion of same, at the point in time that the liquid column 34 is severed, and due to this speed differential the flying liquid column takes a long time to form a spherical shape after severing. For this reason, the liquid column is liable to produce a plurality of satellite droplets before landing.
In a bubblejet type of liquid ejection head, the growth and contraction of the bubble caused by firm boiling simply have the same effects of the pushing and pulling waveforms, respectively, in the piezo type of liquid ejection head. Therefore, essentially, the above-described problems arise in a similar fashion to those of the piezo type of liquid ejection head. In the bubble jet type of liquid ejection head, in general, the bubble firstly grows in a closed state and then the gas inside the bubble contracts suddenly after ejection. As a result of this, the contracting force of the gas acts on the trailing end of the liquid column, and consequently, the liquid column is pulled and stretched.
In the composition described in Japanese Patent Application Publication No. 2003-094662, the liquid is previously split off inside the nozzle flow channel before the start of the ejection operation due to the introduction of gas in the direction perpendicular to the direction of ejection, and it is necessary to supply an extremely large volume of gas in comparison with a micro-bubble having the diameter of several micrometers (μm). Consequently, in actual practice, it takes time to refill the liquid, and the ejection speed declines further when continuous ejection is performed. Furthermore, from the viewpoint of 15 achieving high density of the nozzles, in actual practice it is difficult to install gas tubes for supplying a large volume of gas individually at the nozzles. It is also unavoidable that the liquid droplet volume will become large. Since it is necessary to extract a gas flow channel in some way, then there is also a separate problem in that robustness is poor when the compression of the gas is taken into account.